FEATURESTORY
by Steve Turner
Proper Mulching is One of the Best Things
You Can do for Your Plants
M
ulching is one of the best things you can
do for your plants if done right, but too
much or improperly installed mulch can
be a real problem.
The Problem with Mulch Volcanoes
The common practice of mounding mulch against
the trunk has proven to be a fatal one for many trees.
These often seen “mulch volcanoes” are perfect cir-
cles 8 to 10 inches thick piled against the trunk and
are actually creating more problems than they are
solving. What makes the problem worse is that many
of these trees are on commercial properties under
professional care, and this has helped create the false
impression that this is the proper way to mulch trees.
Homeowners see this and imitate the practice on
their own trees. The neat, clean appearance it gives
a landscape is appealing to many. In fact, I have had
several customers over the years ask me if there is a
mold they can buy to make these volcanoes on their
own trees! So in our quest for a beautiful landscape
we are unknowingly sacrificing the health of the trees
in the long run.
Why Improper Mulching Harms Trees
The bark on the roots of a tree is much different
from the bark on its trunk or branches; it is able to
tolerate moisture as well as the lower oxygen levels
March 2019
in the soil. The above-ground portion of the tree,
which starts at the root flares, has bark that contains
tiny openings which are used to release gases and
toxins from its system. On plants such as cherry trees
or forsythia, these sites are easily seen as tiny white
dots or dashes on the bark and are called lenticels.
Because of this important function, a tree can’t toler-
ate soil or mulch placed above its root flares. The
lack of air and the presence of excess moisture pre-
vents natural respiration from the bark and causes a
buildup of gases and toxins in the bark tissue.
The Damage
If soil or mulch disrupts the respiration of the
bark, the tree will usually respond in one of two
ways. On thin-barked, young trees or species with
naturally thin bark, like beech or linden, this disrup-
tion causes cankers (wounds) on the trunk. These
appear as areas of dead tissue and provide an oppor-
tunity for decay to enter the tree. Other species will
react by sending out additional roots from the trunk.
These roots often end up circling around the trunk
and become girdling roots in the future. Researchers
are now finding out that trees with girdling roots and
excess soil and mulch build-up are much more prone
to snapping off at the base in wind and ice storms.
The longer the problem exists, the more damage oc-
curs, and the chances of correcting it go down.
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